1. Field of the Invention
This invention relates to apparatus for controlling the temperature of gas, and in particular to apparatus which controls the gas temperature by spraying liquid into the gas.
2. Description of Related Art
The concept of spraying liquid into a compression cylinder as a means of absorbing the heat of compression is well known, and is commonly referred to in the art as wet compression. In practice, liquid is sprayed into the cylinder through a nozzle which divides the liquid into a mist of fine droplets. The droplets travel through the gas space and eventually impinge on the cylinder surfaces. While in the gas space, the droplets provide a heat sink which is in intimate contact with the gas being compressed and which has a large surface area allowing heat to be drawn efficiently from the gas and permitting a reasonable rate of compression without an appreciable rise in gas temperature.
German Patent No. DE-52528 describes a technique in which liquid is sprayed over the surfaces of the cylinder to cool the gas during compression.
German Patent No. DE-357858 describes a gas compressor which employs wet compression and uses compressed gas to drive the liquid spray. The outlet of the compression cylinder is connected to an accumulator which temporarily stores compressed gas. The accumulator also contains liquid which is fed, under the pressure in the accumulator, through a single narrow orifice into the compression cylinder via a conduit. The liquid spray is controlled solely by the pressure in the accumulator so that no active control mechanism is required. Liquid is sprayed into the compression cylinder during the whole of the induction stroke and continues to be sprayed into the cylinder during compression until the pressure in the cylinder reaches that in the accumulator.
On the other hand, U.K. Patent No. GB-722524 describes a gas compressor in which liquid is sprayed into the compression cylinder through a plurality of capillary orifices by an independent, hydraulic pump. Compressed air from the compressor is stored in an accumulator and the pressure of the accumulator is used to activate or de-activate the compressor and hydraulic pump simultaneously.
French Patent No. FR-903471 discloses a gas compressor which compresses gas in two stages in compression chambers formed either side of a single piston. The first stage compression cylinder has a concave, conical cylinder head with a single spray injector nozzle at the apex thereof. The second stage compression cylinder on the other side of the piston has an annular cross-section and receives compressed gas from the first stage compression cylinder via an accumulator. A circular channel is formed around the base of the annular cylinder, the upper side of which is formed by a perforated ring. Liquid is fed around the circular channel and is sprayed upwardly into the second stage compression cylinder through the holes in the perforated ring.
U.S. Pat. No. 2,280,845 discloses a gas compressor whose operation is based on the principle of wet compression and in which liquid is sprayed into the gas either in a separate chamber before the gas is passed to the compression chamber or otherwise directly in the compression chamber. In the former case, liquid is sprayed into a separate mixing chamber through nozzles which have an internal helical passage, which imparts rotary motion to water entering the nozzle, so that water ejected from the nozzle spreads out into a cone. This pre-mixing of water with air prior to compression allows the spray to be operated continuously rather than intermittently, i.e. only during compression, which in turn allows the flow capacity of the nozzles to be reduced. In the latter case, liquid is continuously injected directly into the compression cylinder through nozzles extending through the upper end of the cylinder casing. The nozzles each comprise a thin walled spherical head having a number of radially extending coplanar holes providing a fine spray which emerges in a plane parallel to the cylinder head and is confined to a relatively shallow zone at the top of the cylinder. This configuration is said to minimise the percentage of droplets striking the cylinder walls or piston head whilst at the same time maximising the mixing effect since air entering and leaving the cylinder is required to flow through this shallow zone.
A further example of a gas compressor using wet compression is described in Japanese Patent Publication No. 58-183880 and in one embodiment, part of the liquid which is used to compress the gas is sprayed into the compression cylinder during compression through a number of injection valves seated in the cylinder head.
It is also known to use liquid sprays as a means of transferring heat into a gas in a thermodynamic power cycle. For example, hot liquid may be sprayed into an expansion cylinder containing compressed gas, to transfer heat to the gas as it expands. A power cycle which employs this technique is described in EP-0043879.
Examples of apparatus which use liquid sprays to control gas temperature in both compression and expansion processes are described in J. Gerstmann et al, 21st Inter-Society Energy Conversion Engineering Conference, Vol. 1, pages 377-382, U.S. Publication No. 3608311 by Roesel, and the Applicant's U.K. Patent Nos. GB 2283543, GB 2287992, and GB 2300673, the contents of which are incorporated herein by reference.
There are numerous different known techniques and types of spray nozzle for generating a spray of liquid, such as multiple hole spargers as used in fire protection and shower systems, plain orifice, as used in diesel injectors, fan jet nozzles using two impinging jets of liquid, impact or impingement nozzles, pressure swirl nozzles, rotating cup and rotating disk atomisers, ultrasonic atomisers, electrostatic atomisers, and two-fluid nozzles of various kinds involving an air or gas propellant, as used in paint sprayers and aerosol propellant systems.
It is an object of the present invention to provide an improved apparatus for spraying liquid into a chamber to control the gas temperature during compression or expansion thereof.